The invention relates in general to munitions and in particular to Radio Frequency communication with munitions.
Inverted-F antennas (IFAs) are a popular choice for wireless consumer electronics because they can easily be included within circuitry as additional artwork on printed circuit boards (PCBs). Numerous design variations exist to facilitate communication standards such as Wi-Fi.
Antennas are typically used in artillery, mortar, tank, and other munitions for global positioning system (GPS) or telemetry capabilities. Since the bodies of munitions are mostly metal, and since their outer profile must be maintained for flight characteristics, they provide a more challenging antenna placement problem than typical consumer products, whose chassis tend to be made of plastic and which can allow for protruding antennas such as monopole whips or blades.
One antenna solution that is commonly used is to place several patch antennas around the body of the munition in a wrap-around configuration. The main lobe of each patch covers an angular sector around the azimuthal plane of the munition. These antennas can either be individual patches placed in a pocket on the side of the round, or they can be made on a single curved substrate to form an array that is wrapped around the circumference of the munition. The metal body of the munition acts as the ground plane for the patches.
However, there are downsides associated with patch antenna use on munitions. Multiple patch antennas in the form of an array are required in order to provide azimuthal coverage around the projectile, additionally requiring a RF power splitting network. This adds complexity, extra volume, and cost.
Another option is to attempt to cut slots in the body of the munition to form slot antennas. However, as the slot will affect the structural integrity of the munitions, this option is limited to only high frequency communication links where the slot dimensions can be made small.
An alternative option to mounting antennas on the munition body is to attempt to integrate antennas on the very extreme ends of the munitions—the nose or the fins—and use the remainder of the projectile as a ground plane. Using the nose usually requires that the nosecone be made of a plastic material to support an embedded monopole, patch, or scimitar. Additionally, monopole antennas require a full ¼-wavelength of length available at the operating frequency, and additional require an external RF matching network to achieve a nominal 50 ohm input impedance.
A need exists for an improved antenna which may be employed on a munition that is effective but relatively small and inexpensive.